Rail grinding method

ABSTRACT

Method and apparatus for grinding surfaces adjacent the ends of a pair of rail section to be welded together comprising means for holding the rail sections in end-to-end aligned, longitudinal relation. Abrasive grinding means movable about an axis of rotation extending laterally of the rail sections and at an acute angle relative to the longitudinal axis thereof is mounted on carriage means slidable longitudinally of the rail section, and pressure means is provided for moving the abrasive member into contact with the surface of the rail sections during longitudinal travel by the carriage.

United States Patent [191 Behne RAIL GRINDING METHOD Stephen G. Behne, .lanesville, Wis.

Chemetron Corporation, Chicago, 111.

Mar. 29, 1972 Inventor:

Assignee:

Filed:

Appl. No.:

[52] US. Cl 51/326, 51/80 R, 51/178,

51/241 LG Int. Cl B24b 1/00, B24b 46/01, B24b 7/00 Field of Search 51/80 R, 140, 178, 326,

References Cited UNITED STATES PATENTS Fox Peterson June 25, 1974 3,129,535 4/1964 Slattery 51/140 3,566,546 3/1971 Lindmark 5l/l40 3,701,219 10/1972 Sternal 51/140 Primary Examiner-Othell M. Simpson 5 7 1 ABSTRACT Method and apparatus for grinding surfaces adjacent the ends of a pair of rail section to be welded together comprising means for holding therail sections in endto-end aligned, longitudinal relation. Abrasive grinding means movable about an axis of rotation extending laterally of the rail sections and at an acute angle relative to the longitudinal axis thereof is mounted on carriage means slidable longitudinally of the rail section, and pressure means is provided for moving the abrasive member into contact with the surface of the rail sections during longitudinal travel by the carriage.

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The present invention is directed towards a new and improved method and apparatus for grinding contact surfaces adjacent the ends of rail sections, and the like, which sections are subsequently welded into a continuous rail string. In the US. Pat. No. 3,030,494 which patent is assigned to the same assignees as the present invention, there is shown and described a new and improved method and apparatus for forming a continuous rail string and, more particularly, this patent is concerned with a new and improved method and apparatus comprising in combination several separate or individual subassemblies which coact to produce a continuous rail string in a novel manner and more quickly and easily than heretofore has been possible. One of the individual components or subassemblies of the foregoing patent is concerned with the problem of grinding contact surface areas adjacent the ends of the rail sections to be welded together in order that good electrical contact can be made between the rail sections and the electrodes of the rail welding during the welding of the rail sections end to end.

The present invention provides a new and improved method and apparatus for grinding electrode contact surfaces on rail sections and is an improvement over the showing in the aforementioned patent. The electrode contact grinder of the present invention is well suited for use as a component or subassembly in the rail string production system shown in the aforementioned patent. In conjunction with the present invention, a rail welder or welding apparatus such as that shown in US. Pat. No. 3,488,467 may be efficiently used in combination additionally with apparatus for grinding the weld upset produced by the rail welded. A suitable weld upset grinder is shown in US. Pat. No. 3,566,546, and both of these last two mentioned patents are assigned to the same assignee as the present invention.

One of the problems in making a continuous rail string is the fact that the individual rail sections which make up the string, as well as the continuous rail string itself, may have been warped or twisted about the longitudinal axis which make it exceedingly difficult for the rail section surfaces to make good contact with the electrodes in the rail welding apparatus. High pressure contact over a relatively large area is needed for the high ampere current flow in making butt welds, particularly in connection with the rail base which is considerably wider in lateral dimension than the relatively narrow rail head surface which is slightly crowned. In the past it has been a difficult problem to grind suitable planar contact surfaces on those portions of the rail sections with accuracy and consistency so that high amperage current flow between the electrodes can be accommodated with minimum electrical resistance. This is particularly true when the end portions of the individual rail sections or the rail string are twisted about the longitudinal axis. When this occurs it is necessary to make a deeper grind to insure that ample surface area is provided for electrode contact. The problem is more acute with the relatively wide base portion of the rail sections than it is with the crowned head surfaces, however the grinding apparatus and method, in accordance with the present invention eliminates or greatly reduces the foregoing problems and provides for more uniform and better welds in making a continuous rail string than heretofore possible.

It is an object of the present invention to provide a new and improved method for grinding welding electrode, contact surfaces adjacent the ends of rail sections which are to be welded together into a continuous rail string.

Another object of the invention is to provide a new and improved method for grinding parallel welding electrode contact surfaces adjacent the ends of ra il sectior on opposite sides. which surfaces are ground in "156% unifo fm and precise manner even through the rail sections are twisted or warped.

Another object of the present invention is to provide a new and improved method for grinding welding electrode contact surfaces on opposite surfaces of rail sections, which surfaces are precisely parallel and are of ample size to provide for high amperage current flow witli a minimum of contact resistance.

Another object of the present invention is to provide a new and improved method for grinding welding, electrode, contact surfaces on a pair of rail sections to be welded together in single, automatic operation in a minimum of time.

Another object of the present invention is to provide a new and improved rail grinding method system of the character described which provides precision ground welding electrode contact surfaces on opposite sides of the rail sections near their ends.

These and other objects and advantages of the present invention are accomplished in a new and improved method of grinding welding electrode contact surfaces adjacent the ends of rail sections to be welded into a continuous rail string. The method comprises steps of grinding the contact surfaces by the application of abrasive means moving around an axis of rotation extended laterally of an acute angle relative to the longitudinal axis of the rail sections. The area of grinding contact progresses longitudinally of the rail sections toward the ends while the rail sections are held firmly in aligned position and the grinding operation is terminated, spaced short of the end of each rail section.

view taken substantially along line 4-4 of FIG. 1;

FIG. 5 is a fragmentary, horizontal, cross-sectional view taken substantially along 5-5 of FIG. 1;

FIG. 6 is a fragmentary, longitudinal, cross-sectional view taken substantially along line 66 of FIG. 3;

FIG. 7 is a fragmentary, horizontal, cross-sectional view taken substantially along line 7-7 of FIG. 1;

FIG. 8 is a vertical, transverse, cross-sectional view taken substantially along line 88 of FIG. 1;

FIG. 9 is a vertical, transverse, cross-sectional view taken substantially along line 9-9 of FIG. 1;

FIG. 10 is a vertical, cross-sectional view similar to FIG. 6, but illustrating the apparatus with the grinding heads and grinding contact with the rail sections;

FIG. ii is a schematic diagram illustrating in animated fashion the path traversed by the grinding heads relative to the rail sections;

FIG. 12 is a schematic diagram indicating a fluid control system of the apparatus; and

FIGS. l3A-E illustrate in schematic form an electrical control system for the grinding apparatus.

Referring now, more particularly to the drawings, in accordance with the present invention there is provided a new and improved rail grinder referred to generally by the reference numeral in FIGS. 1, 2, and 3. The rail grinder 26 is especially adapted for grinding welding electrode, contact surfaces on opposite surface portions of longitudinal rail sections adjacent the ends thereof so that the rail sections may subsequently be welded together end-to-end in the rail welding apparatus of the type generally shown in US. Pat. No. 3,488,467, previously referred to.

The rail grinder 20 includes a main frame 22 comprising a rectangular, horizontal base structure 24 and a pair of longitudinal side frames 26 extending vertically upwardly along opposite, longitudinal outer edges of the base. As best shown in FIGS. 1, 2, and 3, the base structure 24 is constructed of longitudinal side channels 28 connected at the .ends and intermediate the ends by a plurality of cross members 30.

The rail grinder is mounted for movement along a track comprising a pair of spaced-apart, guide rails 32 and for this purpose pairs of flanged support wheels 34 are mounted on axles 36 supported by the base 24 adjacent opposite ends thereof, as best shown in FIGS. 1 and 2. One of the axles 36 is driven to move the rail grinder along the rails 32 by means of a pair of sprockets 38 and a chain drive 40, which sprockets and chain drive interconnect the axle with a reversible, electrically powered main drive gearmotor 42. The main drive, gearmotor 42 includes a reduction gear assembly so that the axle 36 is driven at relatively low speed and high torque in either direction to move the rail grinder up and down the rails 32 to any selected position.

Each of the side frames 26 of the main frame structure includes a pair of upright corner ports 44 supported from the base 24 and the posts are structurally interconnected at their upper ends by a pair of longitudinally extending, channels 46. Suitable comer braces 48 of angle iron (FIG. 1) are provided to structurally interconnect the posts 44 with the base side channels 28 and with the upper longitudinal channels 46. In addition, transverse cross members 50 are provided at opposite ends of the frame to interconnect the channels 46 and provide a generally rectangular, rigid frame structure.

In accordance with the present invention, the main frame structure 22 provides support for a movable carriage 60 on which is mounted an upper grinding head 70, a lower grinding head 80, and an exit squeeze roll assembly 90. As best shown in FIGS. 1 and 3, the carriage 68 is movable longitudinally on the main frame structure 22 and is guided and supported for longitudinal movement by an upper, carriage support rod 52 and a lower carriage support rod 54. The upper support rod or shaft 52 is supported on one of the longitudinal.

upper channels 46 of a side frame 26 by a plurality of upstanding support brackets 56, as best shown in FIGS. 1 and 3, and the lower support rod 54 is similarly supported by brackets 56 mounted on a lower base side channel 28 as shown. The carriage 60 comprises a pair,

of generally rectangular, vertical side frames 58, each of which includes a pair of spaced-apart corner posts 62 which are interconnected by a plurality of horizontal cross members 64, as best shown in FIG. ll.

The upper ends of the posts 62 of the carriage side frame 58 adjacent the upper support rod 52 are interconnected by a horizontal, elongated hollow tubular member 66 (FIG. 3), which member is secured to the upper support rod 52 for parallel, longitudinal sliding movement with respect thereto by a pair of guide sleeves 68 slidably disposed on the support rod and interconnected to the tubular member by means of laterally extending, parallel side brackets 72, as best shown in FIGS. 1, 2 and 3. Similar cylindrical guide sleeves 68 are mounted on the lower support rod 54, and these sleeves are connected via a bracket 72 to an elongated, hollow, tubular support member 74 connected to the lower ends of the posts 62 on the opposite carriage side frame 58.

From the foregoing description it will be seen that both of the opposite side frames 58 of the movable carriage are supported for longitudinal sliding movement along the respective upper and lower carriage support rods 52 and 54 by means of hollow tubular, upper and lower support members 66 and 74, respectively. The respective side frames 58 in turn are joined by transverse, cross members 76 which structurally tie the side frames together to form an integral relatively rigid box or cagelike carriage base structure.

Movement of the carriage longitudinally on the guide rods 52 and 54 from a centered position of FIGS. 11, 2 and 3 in opposite directions is accomplished by means of a pair of left and right, carriage traverse cylinders 78 and 82 mounted with their rod ends extending outwardly in opposite directions and their closed ends interconnected together, as best shown in FIG. 2. The cylinders are arranged in coaxial alignment of a central longitudinally extending vertical plane of the rail grinder and the outer end of the piston rod of the lefthand cylinder 78 is pivotally interconnected to an upper cross member 56 at the left-hand end of the main frame 22. The outer end of the piston rod of the righthand cylinder 82 is pivotally interconnected to a cross plate 84 disposed transversely between a pair of longitudinally extending angles 86 which are parallel and on opposite sides of the right hand cylinder 82. The angles 86 are secured at opposite ends to the upper, transverse cross members 76 on the carriage frame, as best shown in FIGS. 2, s and 4.

Referring to FIG. 2, when the carriage 60 is in a centered position, the piston rod in the left-hand cylinder 78 is fully extended and the piston rod in the right-hand cylinder 82 is fully retracted. In order to move the carriage to the left of center position, as shown in FIG. 10, pressurized fluid is introduced into the cylinder 78 causing the piston rod to retract inwardly into the cylinder. In order to move the carriage from the carriage left position back to the center position, the flow of pressurized fluid into the cylinder 78 is reversed so that the piston rod is extended outwardly to a fully extended, outward position. To initiate right of center movement of the carriage from the center position to a right of center position (as indicated by dotted lines of the grinding wheels shown in FIG. 10), pressurized fluid is introduced into the right-hand cylinder 82 causing the piston rod to be extended to a fully outward position. To return the carriage to the center position, the fluid flow is reversed to again retract the piston rod in the cylinder 82. From the foregoing it will be seen that the right-hand and left-hand carriage traverse cylinders 78 and 82 control and set up left and right carriage traverse in a direction longitudinally of the grinder in both directions from a centered position. The length of stroke of the piston rod in each cylinder can be readily controlled and adjusted in order to provide the desired amount of carriage travel required.

In accordance with the present invention, the rail grinder 20 is especially adapted for grinding contact spots for welding electrodes on opposite head and base surfaces of a pair of longitudinally aligned railroad rail sections 100 L and 100 R, which sections are subsequently welded together end-to-end to form a continuous rail string. After the spot or contact grinding has been completed by the upper and lower grinding heads 70 and 80 on the traveling carriage 60, the left-hand rail section 100 L, which is attached to the already completed welded rail string is moved to the left by the exit squeeze roll assembly 90, and the right-hand rail section 100 R is moved to the left by a stationary, separate, incoming squeeze roll assembly 110, which assembly is substantially identical in operating structure and characteristics to the exit squeeze roll assembly 90 on the carriage except for the fact that the incoming squeeze roll assembly is mounted on a separate table structure 92 (FIG. 1) positioned in fixed relation, relative to track 32. As described the exit squeeze roll assembly 90 is mounted on and travels with the longitudinally movable main carriage 60.

As viewed in FIGS. 1 and 2, after each new rail section is added to the continuous string of welded together rail sections additional new rail sections 100 R are brought into the grinder 20 from right to left (FIG. 1) and the section 100 L and 100 R are in longitudinal alignment positioned with their ends in closely spaced apart, parallel facing relation as illustrated best in FIGS. 6 and 10. The rail section 100 L on the rail string is moved from right to left by the exit squeeze roll assembly 90 until the right-hand end face is positioned directly beneath a left-hand pointer 94 on the upper grinding head 70, and the incoming squeeze roll assembly 110 is energized to draw a new rail section 100 R into position wherein the left-hand end of the new section is positioned directly beneath a right-hand pointer 96 on the upper grinding head. The pointers 94 and 96 are used to establish a desired spaced-apart relation between the facing ends of the rail sections 100 L and 100 R, which ends are subsequently welded together to form the continuous rail string.

The exit squeeze roll assembly 90 is supported on a platform structure 98 (FIGS. 1, 6 and extending outwardly in cantilever fashion from the left-hand side of the carriage 60, as shown in FIG. 1. The exit squeeze roll assembly is driven by a low speed, high torque, reversible, electrically powered gear motor 102 and the incoming squeeze roll assembly 110 is driven by a similar gear motor 104. Each of the squeeze roll assemblies includes an upright framework 106 having corner posts of angle iron disposed on opposite sides of the path traversed by the rail sections. The comer posts are interconnected by a plurality of horizontal, laterally transverse cross members 112, as best shown in FIGS. 6 and 10 and the corner posts 108 on the same side of the rail sections are joined by horizontal cross members 114. In order to support and move the base of the rail sections 100 L and 100 R, each squeeze roll assembly includes a lower, drive roll 116 carried on a drive axle 118, which is supported in suitable bearing assemblies at opposite ends and driven by a respective gear motor 102 or 104, as best shown in FlG. 8.

Both squeeze rolls 90 and 110 serve a dual purpose in moving the rail sections longitudinally to desired positions and clamping or holding the rail section in precise longitudinal alignment. In order to insure positive driving and holding contact between the base of the rail sections and the drive rolls 116, each squeeze roll assembly includes an upper, pressure roll 120 adapted to contact the head surface of the rail sections to urge the rail sections downwardly so that the base is in firm driving contact with the drive rolls 116. The upper pressure rolls 120 are supported on horizontal axles 122, which axles are supported for free rotation at opposite ends by bearing assemblies 124. The bearing assemblies 124, in turn, are mounted on horizontal, vertically adjustable, support base structures 126. The support base structures 126, are mounted for a vertical translation within the upright frame structures of the squeeze rolls and for this purpose each base structure includes a pair of cylindrical sleeves 128 at opposite ends, which sleeves are slidably disposed on a pair of guide rods 130 supported in parallel, vertical alignment on the inside of the upright frame structures 106 by bearing assemblies 132 at the upper and lower ends, as best shown in FIG. 8. From the foregoing, it will be seen that the pressure rolls and drive rolls are joumaled about parallel, vertically spaced, horizontal axes and that the upper, pressure rolls are adjustably positioned to move vertically toward and away from the lower drive rolls 116, thereby to hold or release pressure on the rail sections for driving and/or supporting and holding the rail sections in precisely aligned contact between each pair of upper and lower rolls.

Vertical translation of the upper pressure rolls 120 is accomplished by a pair of pneumatic cylinders 134 and 136 provided on the respective squeeze rolls 90 and 110 and the outer or downward end of the vertical piston rod of each cylinder is pivotally interconnected with the roll supporting base structure 120 which is slidable up and down on the guide rods 130. Fluid flow into and out of the upper and lower ends of the cylinders moves the upper pressure rolls 120 into and out of contacting engagement with the heat surface of the rail sections as required. For clamping the rail sections tightly fluid is directed into the upper end of the cylinders 134 and 136 holding the rail sections down against the lower drive rolls 116 so that upon energization of the squeeze roll gear motors 102 and/or 104, the rail sections will be moved in the desired direction.

As will be developed hereinafter the squeeze roll gear motors are provided with a braking mechanism used to prevent rotation of the lower drive roll 116 for the purpose of restraining the rail sections against longitudinal translation during a grinding operation as the grinding heads and mounted on the movable carriage 60 traverse back and forth. It should also be appreciated that while the upper pressure rolls are biased downwardly into pressure engagement against the head surface of the rail sections, the rail sections are restrained against vertical and laterally horizontal movement, however, longitudinal translation is permitted when desired by releasing the braking mechanism of one or both gear motors 102 and 104. When the carriage 60 is moved longitudinally on the supporting main frame structure 22 during a cycle of grinding head operation, the braking mechanism of exit squeeze roll assembly 90 is released and the left-hand rail section 100 L is restrained against longitudinal translation by clamping means on the other components in the system acting on the rail string such as the welder or another external clamping device. The upper pressure rolls 120 of the squeeze roll assemblies are freely rotatable and may rotate in response to longitudinal translation of the carriage 60 or upon driving rotation of the lower drive rolls 116.

In addition to the support and the vertical and horizontal alignment and guidance of the rail sections 100 L and 100 R provided by the exit and incoming squeeze rolls 90 and 110, support is also provided by a pair of rolls 138 (best shown in FIGS. 4, 6 and mounted on shafts which are joumaled for rotation by pillow blocks 140 carried on horizontal base platforms 142 provided on the carriage 60. As best shown in FIGS. 4,

5, 6 and 10, the bases 142 are supported from laterally transverse cross members 76 which extend between comer posts 62 of the traveling carriage 60. As viewed in FIG. 4, it will be seen that the base or bottom surfaces of the rail section 100 L and 100 R roll over and are supported on the freely rotatable guide rolls 138 as the rail sections move longitudinally relative to the carriage. Lateral guidance of the rail sections with respect to the carriage is provided by pairs of web engaging guide rolls 144, best shown in FIGS. 4 and 5. The web guide rolls 144 are mounted on vertical axles which are joumaled in fixed and movable support bracket assemblies 146 and 148, respectively, best shown in FIGS. 3, 4, 5 and 6.

In accordance with the present invention, the upper grinding head 70 includes an upper grinding wheel 150 which comprises a plurality of cylindrical discs or wheels formed of abrasive material and mounted on a common shaft 152. The shaft 152 is supported by pillow block bearings 158 at opposite ends mounted on a pair of support angles 156 (FIG. 4) attached to a rectangular motor base 154 formed of angle iron. The grinding wheel shaft 152 is driven at relatively high speed by an electric motor 160 via a belt drive 162.

The motor base 154 is supported for vertical, relative movement on a rectangular, upper grinding head frame 164 formed of channel iron. A plurality of vertical guide rods 166 are secured at their upper and lower opposite ends in pillow blocks 168 attached to the inside web of the grinding head frame 164 and the motor base 154 is provided with a plurality of bearing sleeves 170 on the sides thereof slidably disposed on the guide rods 166, thus permitting relative vertical adjustment between the motor base 154 and the grinding head frame. The frame 164 in turn is mounted for vertical movementor translation on the carriage '60, and for this purpose, vertical guide rods 172 are provided on the opposite side frames 58 of the carriage. The guide rods are supported at opposite ends by pillow blocks 174 secured to the cross members 64, of the carriage side frames, as best shown in FIGS. 3 and 4. Opposite side members of the upper grinding head frame 164 are provided with cylindrical sleeves 176 which are slidably disposed on the vertical guide rods 172 to permit relative vertical sliding movement of the frame 164 on the carriage 60.

Control and vertical sliding movement of the upper grinding head frame 164 on the carriage 60 is accomplished by a pair of upper grinding head cylinders 178, and the piston rods thereof are pivotally interconnected to the grinding head frame by means of clevis and bracket attachments as best shown in FIGS. 6, 10 and 3. The upper, closed ends of the cylinders are pivotally connected to transverse cross members 76 of the carriage 60 so that when pressurized fluid is introduced into either end of the cylinders the frame 164 can be moved upwardly or downwardly on the carriage into or out of grinding engagement with the head surface of the rail sections L and 100R.

In order to adjust the vertical position of the upper grinding wheel relative to the upper head surface of the rail sections 100 Land 100 R, the upper grinding head 70 includes a pair of upper pressure rolls 180 disposed on opposite sides of the grinding wheel axis of rotation as best shown in FIGS. 6 and 10. Each pressure roll is mounted on an axle 182 parallel of the grinding wheel axle 152 and the axles 182 are supported at opposite ends from the grinding head frame 164 by means of support bearing assemblies 184, as best shown in FIGS. 6 and 10. From the foregoing it will be seen that the pressure rolls 180 are in a fixed vertical position relative to the main frame 164 of the upper grinding head 70 while the grinding wheel 150 itself is vertically adjustable with respect to the main frame in order to compensate for wear on the grinding wheel which occurs in consequence of the length of time that grinding engagement with the rail head surfaces of the rail section occurs. For the purpose of moving and adjusting for wear on the grinding wheel 150, the upper grinding head 70 is provided with a control assembly for moving the motor frame 154 relative to and with respect to the main grinding head frame 164. The upper grinding head includes a rectangular adjusting frame 186 which is pivotally secured along one side by means of several pivot pin support assemblies 188 attached to a side member of the main grinding head frame 164 as best shown in FIG. 7. Longitudinal side members 190 of the adjusting frame 186 are pivotally interconnected with parallel side members of the motor base 154 through pivot pin connector assemblies 192 for raising and lowering the motor base 154 with respect to the main grinding head frame 164. Control of the pivotal relation between the pivotable adjusting frame 186 and the vertically movable motor base frame 154 is provided by means of a screw jack 194 (FIGS. 6 and 10). The screw jack is threadedly connected to one side member of the adjusting frame 186 and is mounted in vertical position for rotation in either direction to raise or lower the angle of adjusting frame relative to the main grinding head frame. The jack screw is supported in a guide sleeve 196 fastened to a transverse side member of the main grinding head frame 164 and rotation of the jack screw in either direction by a controlled amount is accomplished by means of a slow speed, electric driven, gear motor 198. The adjusting gear motor is mounted on the same transverse side member of the main grinding head frame 164 as the sleeve 196 and is coupled to rotate the jack screw 194 when the motor is energized. From the foregoing, it will be seen that when the adjusting gear motor 198 is driven to rotate in either direction, the grinding wheel 150 is moved up and down relative to the main grinding head frame 164 and the pressure rolls 180 in order to compensate for wear occurring on the grinding wheel 150. When the pressure rolls are moved downwardly into contact against the head surface of a rail section by the cylinders 178, grinding will be effected by the fast moving outer periphery of the grinding wheel 150 and the depth of grind is controlled by the adjusting gear motor 198. As wear occurs on the grinding wheel, the depth of grind will diminish correspondingly and to compensate for this wear, the adjusting gear motor 198 is energized for a selected period or number of revolutions to lower the grinding wheel 150 to provide the same desired depth of grind or grinding pressure as originally set up.

In accordance with the present invention, the lower grinding head 80 includes an abrasive grinding wheel 200 comprising a plurality of grinding wheel discs mounted on a common shaft 202. Rather than a perpendicular alignment with respect to the rail sections as the upper shaft 152 is set up, the lower shaft is aligned at an acute angle with respect to the longitudinal axis of the rail sections as best shown in FIG. and while both the upper and lower grinding wheel shafts are horizontal, they are not parallel. The lower grinding wheel 200 is adapted to move upwardly into contact against the under surfaces of the base of the rail sections and it has been found that by adjusting the axis of rotation of the grinding wheel away from a perpendicular to a lateral direction to an acute angle relative to the longitudinal axis of the rail section better grinding occurs. With the upper shaft 152 laterally perpendicular and horizontal, and the lower shaft 202 horizontal but at an acute angle in a lateral direction with respect to the longitudinal axis of the rail sections slight variations comprising twists or winds in the rail sections are better compensated for as the spot grinding occurs. The clamping efi'ect on the rail sections between the upper and lower grinding wheel moving longitudinally toward the ends of the rail sections produces welding electrode contact surfaces that are exactly parallel. Except for the difference in angular arrangement of the grinding wheel axle with respect to the longitudinal axis of the rail sections, the lower grinding head 80 is substantially similar to the upper grinding head 70 and includes a pair of pressure rolls 204 disposed on opposite sides of the guiding wheel 200 for guiding contact with the rail base. The guiding wheel axle 202 is supported on a pair of pillow block bearings 206 mounted on a pair of angles 208 which are attached to a rectangular lower motor base frame 210 formed of angle iron. The lower motor base frame 210 is mounted for vertical sliding movement with respect to a larger lower grinding head main frame 212 formed of channels and of rectangular shape as shown. The lower motor base frame 210 is supported for vertical sliding movement with respect to the lower grinding head main frame 212 by a plurality of vertical guide rods 214 secured to the inside surface of the main frame by bearing blocks 216 at opposite ends of the guide rods. Sleeves 218 are mounted for' sliding disposition on the guide rods 214, and the sleeves are attached to side members of the motor base frame 210 so that the motor base frame is slidable in continuously parallel and vertical translation with respect to the lower grinding head main frame. The grinding head main frame in turn is mounted for vertical translation with respect to the carriage 60 on vertical glide rods 220 supported at opposite ends by bearing blocks 222 attached to the carrier side frame cross members 64, as best shown in FIG. 4.

Opposite side members of the lower grinding head frame are provided with sleeves 224 slidably disposed on the guide rods 220, as best shown in FIGS. 3, 4 and 5, and the lower grinding head main frame is controlled for movement up and down on the transverse carriage 60 by means of a pair of lower grinding head control cylinders 226 having the upper ends of their piston rod pivotally connected to the grinding head main frame through connector bracket 228, as best shown in FIGS. 6 and 10. The lower ends of the lower head control cylinders are pivotally connected to transverse cross members 76 of the carriage 60 as shown in FIG. 4, so that the introduction of fluid under pressure into the lower ends of the cylinders elevates the lower grinding head 80 on the carriage 60 and a reverse flow of the fluid into the cylinder provides for a lowering of the grinding wheel 200 away from contact with the base of the rail sections. The lower grinding wheel is driven by an electric motor 230 secured to the underside of a motor base 210 and the motor is drivingly interconnected with the lower grinding head shaft 202 via a belt drive 232.

When pressurized fluid is introduced into the lower end of the lower grinding head control cylinders 226, the grinding head main frame 212 is moved upwardly on the carriage 60 until the lower grinding head pressure rolls 204 contact the underside of the rail sections L and 100 R. Adjustment of the depth of grind is controlled by means of a motor driven jack screw 234 supported for rotation in a vertical bearing assembly 236 mounted on the inside of a transverse cross member of the grinding head main frame. The lower end of the jack screw is pivotally connected to a transverse side member of a lower adjusting frame 238 and the upper end of the jack screw is driven to rotate in either direction at a low speed by means of a lower grinding head adjusting gear motor 240. The electrically powered gear motor 240 supplies high torque in either direction to control the upward or downward movement of the grinding wheel 200 relative to the frame 212. As best shown in FIGS. 3 and 4, the lower adjusting frame 238 is pivotally secured to the grinding head main frame by hearing bracket assemblies 224 mounted on a transverse member opposite the side member connected to the jack screw 234. Side members of the adjusting frame 238 generally parallel with the side frames 58 of the carriage 60 are pivotally interconnected to the lower grinding head motor base 210 through bearing block and bracket assemblies 244 so that as the lower jack screw 234 is driven to rotate in either direction, the motor base 210 is moved up or down relative to or with respect to the lower grinding head main frame 212 in order to adjust the depth of grind and compensate for grinding wheel wear.

From the foregoing, it will be seen that the depth of grind of the upper grinding wheel and lower grinding wheel 200 is controlled and adjustable by means of upper and lower grinding head adjustment motors 198 and 240, respectively. Guiding contact between the upper and lower grinding heads and the upper and lower surfaces of the rail sections is provided by the upper and lower pressure rolls and 204, as shown in FIGS. 6 and 10 and movement of the upper and lower grinding heads into and out of grinding engagement with the rail sections is controlled by a pair of cyl- 

1. A method of grinding a contact surface adjacent the end of a rail section which is welded in a rail string comprising the steps of grinding said surface by the application of a set of a plurality of relatively narrow width abrasive wheels mounted side by side on a common axle and driven to rotate around an axis of rotation aligned transversely and at an acute included angle relative to the longitudinal axis of said rail section; moving said axis of rotation longitudinally of said rail section while said abrasive is in grinding contact with said rail section, and moving said abrasive wheels transversely away from grinding engagement with said rail section prior to reaching the end thereof.
 2. The method of claim 1 including the step of restraining said rail section against movement during said grinding contact by the application of clamping force applied at a location spaced from said end of the rail section on the other side of the grinding contact.
 3. The method of claim 2 wherein said clamping force is applied at a location movable longitudinally of said rail section as said axis of rotation moves.
 4. The method of claim 1 including the step of simultaneously grinding an opposite surface on said rail section by the application of a plurality of said abrasive wheels mounted side by side on a common axle and driven to rotate around a second axis of rotation extending laterally transverse of said longitudinal axis and at an acute angle relative to said first mentioned axis of rotation.
 5. The method of claim 4 wherein said first mentioned abrasive is applied to the base of said rail section and said second mentioned abrasive is applied to the head of said rail simultaneously therewith.
 6. The method of claim 1 including the steps of moving said plurality of abrasive wheels transversely into grinding contact with said rail section before movement of sAid axis longitudinally toward said end of said rail section and moving said plurality of abrasive wheels transversely out of grinding contact with said rail section before reaching said end thereof.
 7. A method of grinding electrode contact surfaces adjacent the ends of a pair of rail sections to be welded together end to end in a rail string comprising the steps of longitudinally aligning said rail sections with adjacent ends spaced apart a selected distance; applying a pair of sets of a plurality of rotating abrasive wheels side by side and driven on a common axle to opposite surfaces on one rail section and moving the area of abrasive application longitudinally toward the end of said one section; maintaining the axle of at least one of said sets of a plurality of abrasive wheels at an acute included angle transverse to a longitudinal axis of said rail sections during said abrasive application; disengaging the sets of abrasive wheels from contact with said one rail section after a preselected amount of longitudinal traverse toward the end of said one rail section prior to reaching said end.
 8. The method of claim 7 wherein one set of a plurality of abrasive wheels applied to one of said opposite surfaces of said one rail section is moving in a path parallel of the longitudinal axis of said section while the other set of a plurality of abrasive wheels applied to an opposite surface of said one section is moving in a path at an acute angle with respect to said longitudinal axis of said one section.
 9. The method of claim 7 including the successive steps of moving said sets of abrasive wheels longitudinally away from an end of the other of said rail sections, moving said sets of abrasive wheels into grinding engagement with opposite surfaces on said other section, and moving the area of abrasive contact longitudinally toward said end of said other rail section.
 10. The method of claim 9 including the step of disengaging the sets of abrasive wheels from contact with said other rail section before reaching said end. 